• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.6
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• pp.1881-1900
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• 2014

Since 802.11 wireless LANs are so widely used, it has become common for numerous access points (APs) to overlap in a region, where most of those APs are managed individually without any coordinated control. This pattern of wireless LAN usage is called the private OBSS (Overlapping Basic Service Set) environment in this paper. Due to frame collisions across BSSs, each BSS in the private OBSS environment suffers severe performance degradation. This study approaches the problem from the perspective of congestion control rather than noise or collision resolution. The retry limit, one of the 802.11 attributes, could be used for traffic control in conjunction with TCP. Reducing the retry limit causes early discard of a frame, and it has a similar effect of random early drops at a router, well known in the research area of congestion control. It makes the shared link less crowded with frames, and then the benefit of fewer collisions surpasses the penalty of less strict error recovery. As a result, the network-wide performance improves and so does the performance of each BSS eventually. Reducing the retry limit also has positive effects of merging TCP ACKs and reducing HOL-like blocking time at the AP. Extensive experiments have validated the idea that in the OBSS environment, reducing the retry limit provides better performance, which is contrary to the common wisdom. Since our strategy is basically to sacrifice error recovery for congestion control, it could yield side-effects in an environment where the cost of error recovery is high. Therefore, to be useful in general network and traffic environments, adaptability is required. To prove the feasibility of the adaptive scheme, a simple method to dynamically adjust the value of the retry limit has been proposed. Experiments have shown that this approach could provide comparable performance in unfriendly environments.

• Journal of Korean Society on Water Environment
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• v.21 no.3
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• pp.256-262
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• 2005

The purpose of this study is to investigate the performances of organic removal and methane recovery by using a full scale two-phase anaerobic system. The full scale two-phase anaerobic process was consists of an acidogenic anaerobic baffled reactor (ABR) and a methanognic upflow anaerobic sludge blanket (UASB) reactor. The volumes of acidogenic and methanogenic reactors were designed to $28.3m^3$ and $75.3m^3$. The two-phase anaerobic system represented 60-82% of COD removal efficiency when the influent COD concentration was in the range of 7,150 to 16,270 mg/L after screening (average concentration is 10,280 mg/L). After steady-state, the effluent COD concentration in the methanogenic reactor showed $2,740{\pm}330 mg/L$ by representing average COD removal efficiency was $71.4{\pm}8.1%$ when the operating temperature was in the range of $19-32^{\circ}C$. The effluent SCOD concentration was in the range of 2,000-3,000 mg/L at the steady state while the volatile fatty acid concentration was not detected in the effluent. Meanwhile, the COD removal efficiency in the acidogenic reactor showed less than 5%. The acidogenic reactor played key roles to reduce a shock-loading when periodic shock loading was applied and to acidify influent organics. Due to the high concentration of alkalinity and high pH in the effluent of the methanogenic reactor, over 80% of methane in the biogas was produced consistently. More than 70% of methane was recovered from theoretical methane production of TCOD removed in this research. The produced gas can be directly used as a heat source to increase the reactor temperature.

• Journal of the Korean Society of Clothing and Textiles
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• v.35 no.6
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• pp.700-711
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• 2011

The purposes of the study were to identify the online service attributes that contribute to online consumer experiences of satisfaction, service failure, and service recovery and to examine whether differences exist in these attributes between U.S. and Korea. E-A-S-QUAL provided a useful framework for the study. Focus group interviews and web surveys were conducted by utilizing college students in both countries. No significant cultural differences were found in online service dimensions of service satisfaction. Personalization was the most frequently mentioned online service dimension of service satisfaction both in the U.S. and Korea. The findings showed significant cultural differences in terms of online service dimensions responsible for service failure and recovery. For Korean consumers, merchandising was one of the key online service dimensions of service failure, while efficiency was the important service dimension resulting in service failure for the U.S. consumers. In addition, for U.S. consumers, efficiency and personalization were the two most frequently mentioned service dimension for service recovery, while Korean consumers put more importance on the contact and information dimensions for service recovery. This study provided a comprehensive list of online service attributes important to online apparel retailing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3B
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• pp.130-137
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• 2005

Wireless communication environment is changing rapidly as we use new wireless communication technology such as WiBro to access high speed Internet. As a result, reliable data transmission using TCP is also expected to increase. Since TCP assumes that it is used in wired network, TCP suffers significant performance degradation over wireless network where packet losses are related to non-congestion loss. Especially RTO imposes a great performance degradation of TCP. In this paper, we analyze the loss recovery probabilities based on previous researches, and use simulation results of our algorithm to show that it prevents performance degradation by quickly detecting and recovery losses without RTO during fast recovery.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.403-406
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• 2003

In this paper, we have proposed a carrier recovery algorithm of OFDM/QPSK-DMR(Orthogonal Frequency Division Multiplexing/Quadrature Phase Shift Keying Modulation-Digital Microwave Radio)system using BL-PSF(Band Limited-Pulse Shaping Filter) and have analyzed the carrier phase MSE(Mean Square Error) performance of OFDM/QPSK and single carrier DMR systems. The existing OFDM/QPSK-DMR system using windowing requires training sequence or CP(Cyclic prefix) to synchronize a receive. carrier frequency. Because in the OFDM/QPSK-DMR system using BL-PSF there is no training sequence or CP(Cyclic Prefix), we also propose a carrier recovery useful to the system. The simulation results confirm that the proposed carrier recovery algorithm has the same carrier phase MSE(Mean Square Error) performance for the single carrier DMR system under AWGN(Additive White Gaussian Noise) environment.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.394-397
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• 2003

In this paper, we have proposed a clock recovery algorithm of OFDM/QPSK-DMR(Orthogonal Frequency Division Multiplexing/Quadrature Phase Shift Keying Modulation-Digital Microwave Radio)system using BL-PSF(Band Limited-Pulse Shaping Filter) and have analyzed the clock phase error variance performance of OFDM/QPSK and single carrier DMR systems. The existing OFDM/QPSK-DMR system using the windowing requires training sequence or CP(Cyclic Prefix) to synchronize a receiver clock frequency Because there is no training sequence or CP(Cyclic prefix) in our proposed DMR system, the proposed clock recovery algorithm is useful to the OFDM/QPSK-DMR system using BL-PSF, The simulation results confirm that the proposed clock recovery algorithm has the same clock phase error variance performance in a single carrier DMR system under AWGN(Additive White Gaussian Noise) environment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.12
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• pp.1702-1714
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• 1998

Removal of spilled oil over the sea and the river has become one of the urgent problems in these days. Removing oil using mechanical devices was recommended because chemical dispersion could cause the secondary contamination in the environment. In the present study a series of experiments were carried out to study the effect of operating conditions, especially, the angle between the belt and the fluid surface on the rate of recovery for the spilled oil using a belt skimmer. Three different types of operation, namely, upward pickup, downward pickup and up-and-downward pickup situations have been investigated for various contact angles, belt speeds and oil thicknesses to find the effects on the recovery rate. The highest rate of oil recovery was found in the case of a contact angle of $45^{\circ}$ and downward pickup. Furthermore, an optimal belt speed was found to reach the saturated recovery rate for a given oil thickness.

• Journal of Korean Academic Society of Home Health Care Nursing
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• v.27 no.3
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• pp.344-355
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• 2020

Purpose: Recovery has a growing influence on policy for individuals with mental illness and their families. This study was designed to examine the meaning of recovery from the perspectives of community-dwelling patients with mental illness and their families. Methods: Using a descriptive qualitative approach, in-depth, face-to-face interviews were conducted on 24 adults (14 patients with mental illness and 10 family members). All interviews were audiotaped, transcribed and analyzed using thematic analysis. Results: The findings showed that recovery for the patients with mental illness suggested gradual changes by individual will and self-awareness, the relationship with both their family and self-help group, and the support of a therapeutic environment. Seven primary themes emerged from the analysis: improving insight on illness, strong will toward hope, discovering changed myself, helping each other together, gradual influence of positivity, being oriented to a therapeutic setting, and recognizing of home as a calm place. Conclusion: The findings of this study revealed that based on the conceptual elements of recovery of the patients with mental illness and their families, we expect to improve the systematic, comprehensive, and quality mental health services.

• Nuclear Engineering and Technology
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• v.53 no.7
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• pp.2357-2363
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• 2021

Silicon carbide is widely used in radiation environments due to its excellent properties. However, when exposed to the strong radiation environment constantly, plenty of defects are generated, thus causing the material performance downgrades or failures. In this paper, the two-temperature model (2T-MD) is used to explore the defect recovery process by applying the electronic energy loss (Se) on the pre-damaged system. The effects of defect concentration and the applied electronic energy loss on the defect recovery process are investigated, respectively. The results demonstrate that almost no defect recovery takes place until the defect density in the damage region or the local defect density is large enough, and the probability of defect recovery increases with the defect concentration. Additionally, the results indicate that the defect recovery induced by swift heavy ions is mainly connected with the homogeneous recombination of the carbon defects, while the probability of heterogeneous recombination is mainly dependent on the silicon defects.

• Proceedings of KOSOMES biannual meeting
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• 2005.11a
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• pp.165-170
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• 2005

A basic study for the development of a disk type oil skimmer for a tank lorry, compares via experiments to the oil recovery differences by material between the existing oil skimmer disk and several discs which oil adhesion are possible. The experiment results in this study are summarized as follows: In all the disks, the mass of recovery of bunker-A oil was greater than light oil. In light oil, there was nearly no differences in the mass of oil recovery by disk material, but in the case of bunker A oil, recovery efficiency showed big differences depending on the disk materials. For light oil, the differences in the mass of oil recovery per unit of operation time from the initial time zone were hardly shown. However, the mass of recovery of bunker-A oil linearly increased from the initial operation time in all the disks and the increase shaped a slow moving trend as time went on; therefore, the mass of oil recovery per unit of operation time showed differences depending on time. This result shows that oil viscosity has an effect on the disk recovery efficiency. When comparing the mass of pure oil recovery and the mass of water recovery in the total mass of recovery by bunker-A oil, there was no difference in the mass of oil recovery between the window-aluminum material disk and the disks consisting of other materials, but the mass of water recovery of the former was relatively very small. This shows the most ideal result in view of oil recovery efficiency that considers the mass of water recovery. In conclusion, it was found that aluminum is the most advantageous as the material for tank lorry oil skimmer disk.